The microbial ecology of Sub-Antarctic tundra soils
The microbial ecology of tundra soils was studied at four contrasting
sites on the sub-Antarctic island of South Georgia. Two main
study sites were used - a deep Mossbank dominated by Polytrichum
alpestre/Chorisodontium aciphyllum and a Festuca contracta Grassland,
and two subsidiary sites - a dense stand of the deciduous Dwarf Shrub
Acaena magellanica and a Tortula robusta/Rostkovia magellanica Mire
included for certain aspects of this two year programme.
The viable bacterial and fungal populations of the main sites
were comparable to those of other tundra regions and showed a similar
decrease with depth. Intra-site variability was correlated with
vegetation cover and increased microbial populations associated with
Juncus scheuchzerioides at the Mossbank and Festuca contracta at the
Grassland. Seasonal variability of the microbial populations showed
complex correlations with a range of edaphic variables of which
temperature and moisture were the most important. Direct bacterial
counts showed high numbers present. Variability in total numbers was
reflected in the viable counts.
Cellulolytic bacteria and fungi and ligninolytic fungi, a small
but consistent part of the microbial populations, were correlated with
depth, moisture and the heterotrophic populations but showed little
association with the vegetation cover. Chrysosporium sp. and pycnidial
fungi were important celluloytic organisms found at both main sites.
Sterile mycelia were frequently isolated.
The decomposition of moribund moss in the Mossbank was very slow
(3-5% p.a.) while dead grass culms in the Grassland showed rates of
The decomposition rates of a pure cellulose material were compared
at all four sites and showed the order of cellumlytic activity
to be: Dwarf Shrub>Mire>Grassland>Mossbank. Patterns of cellulose
decomposition revealed differences between the sites with depth and
season and correlation analyses showed associations with vegetation at
the Grassland and Mire sites.
Total potential activity of the four sites was assessed by
respirometry. The expression of results was complicated by the
differing organic contents of the soils. The Dwarf Shrub and Mire
sites showed consistently greater oxygen consumption than the Grassland
or Mossbank and all sites showed reduced respiration with depth.
Correlation analyses showed moisture to be the most important seasonal
factor and at the Mossbank respiration was correlated positively with
J. scheuchzerioides and negatively with P. alpestre.
A general model linking decompositioA and nutrien~ cycling was